1. Field of the Invention
The present invention relates to a method to transfer a circuit pattern to a substrate, and more particularly to a method which transfers the circuit pattern to the substrate by two patterns different from the circuit pattern.
2. Description of the Prior Art
In semiconductor manufacturing processes, in order to transfer an integrated circuit layout onto a semiconductor wafer, the integrated circuit layout is first designed and formed as a lithography pattern. Then, the lithography pattern is transferred to form a photo mask pattern. The photo mask pattern is then proportionally transferred to a photoresist layer positioned on the semiconductor wafer.
As a design pattern of an integrated circuit becomes smaller, for example, a critical dimension becomes smaller than 90 nm, and due to a resolution limit of an optical exposure tool, an optical proximity effect occurs during the photolithographic process performed for transferring the photo mask pattern with high density. The optical proximity effect causes defects, such as residue of an assistant feature next to a right-angle main feature, right-angle corner rounding, line end shortening, and line width increasing/decreasing to the photo mask pattern during transferring.
Contact/via hole patterns having small dimensions have the strictest pattern transfer requirements among all circuit patterns. In addition, when spaces between two adjacent element patterns are different, and the element patterns, comprising both dense patterns and iso patterns, are disposed randomly, the process window of the lithography process is decreased.
To avoid the above-mentioned problems caused by the optical proximity effect, resolution enhancement technology (RET) and optical proximity effect correction (OPC) are developed. RET technologies used widely in the semiconductor industry include: sub-resolution assist feature (SRAF), off-axis illumination, and phase shift mask. However, the above-mentioned methods require complicated simulations, and changes in light source, photoresist, and equipment. Moreover, when the patterns are disposed randomly, RET becomes complicated due to the deviation between the dense patterns and the iso patterns, and pattern transfer defects will occur.